Building control systems are employed to regulate and control various environmental and safety aspects of commercial, industrial and residential facilities (hereinafter referred to as “buildings”). In ordinary single-family residences, control systems tend to be simple and largely unintegrated. However, in large buildings, building control systems often consist of multiple, integrated subsystems employing hundreds of elements.
For example, a heating, ventilation and air-conditioning (“HVAC”) building control system interrelates small, local control loops with larger control loops to coordinate the delivery of heat, vented air, and chilled air to various locations throughout a large building. Local control systems may use local room temperature readings to open or close vents that supply heated or chilled air. Larger control loops may obtain many temperature readings and/or air flow readings to control the speed of a ventilation fan, or control the operation of heating or chilling equipment.
As a consequence of the interrelationship of these control loops, many elements of a building control system must communicate information to each other. To this end, communication networks have been incorporated that transmit digital data between and among the various elements in accordance with one or more sets of protocols. By way of example, one or more local area networks using Ethernet or other standard protocols are often used to effect communication between elements and subsystems.
A drawback to the current state of HVAC systems is the amount of wiring involved in connecting all of the elements of the system in a large building. A large building may have hundreds of sensors, room controllers, and actuation devices. All of these elements must be interconnected in some manner so that both local and overall control operations may be carried out. Installation of the large number of wires required to accomplish such interconnection is labor intensive, and requires significant material cost.
As a consequence, there is a need for a building control system that reduces the wiring requirements of the current systems.